Golf ball

ABSTRACT

A golf ball having a spherical core, a mid layer covering this core, a reinforcing layer covering this mid layer, and a cover covering this reinforcing layer, wherein the base polymer of the mid layer includes a styrene block-containing thermoplastic elastomer and an ionomer resin; the mid layer has a hardness as measured with a Shore D type hardness scale of equal to or less than 54; the mid layer has a thickness of 0.5 mm or greater and 1.6 mm or less; and the base polymer of the reinforcing layer is a reaction product between carboxyl group-containing polyurethane and polycarbodiimide. The principal component of the base polymer of the cover is an ionomer resin. The cover has a hardness as measured with a Shore D type hardness scale hardness of equal to or greater than 55 and the cover has a thickness of equal to or less than 1.2 mm.

CROSS REFERENCE

The present application is a 37 C.F.R. §1.53(b) continuation of, and claims priority to, U.S. application Ser. No. 11/362,127, filed Feb. 27, 2006. Priority is also claimed to Japanese Patent Application No. 2005-073295 filed on Mar. 15, 2005 and Japanese Patent Application No. 2005-076551 filed on Mar. 17, 2005. The entire contents of these applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to golf balls. More particularly, the present invention relates to multi piece golf balls having a core, a mid layer and a cover.

2. Description of the Related Art

Top concern to golf players for golf balls is their flight performances. The golf players particularly place great importance on flight distance attained upon shots with a driver. Feel at impact is also important to golf balls. Golf players prefer soft feel at impact. Furthermore, durability is also important to golf balls. Golf balls not accompanied by breakage upon repeated impacts have been desired.

In light of flight performances and feel at impact, golf balls having a variety of structures have been proposed. U.S. Pat. No. 6,106,415 (JP-A No. H10-179795) discloses a golf ball in which either one of the mid layer or the cover comprises an ionomer resin while the other comprises polyurethane. U.S. Pat. No. 6,231,460 (JP-A No. H11-253581) discloses a golf ball having amid layer comprising a thermoplastic polyurethane elastomer, and a cover comprising an ionomer resin. US2003/083155 (JP-A No. 2003-52857) discloses a golf ball having a mid layer comprising a thermoplastic elastomer, and a cover comprising an ionomer resin. U.S. Pat. No. 6,106,415 (JP-A No. 2001-585) discloses a golf ball having amid layer comprising an urethane resin, and a cover comprising an ionomer resin.

Ionomer resins are inferior in compatibility with other resins. Ionomer resins are particularly inferior in compatibility with thermoplastic elastomers. In golf balls having a cover comprising an ionomer resin and a mid layer comprising other resin, adhesion between the mid layer and the cover may be insufficient. In this type of golf ball, repeated impacts may result in detachment of the cover from the mid layer. The detachment leads to breakage of the golf ball. In particular, according to golf balls having a thin mid layer or a thin cover, breakage is apt to be caused due to insufficient adhesion. An object of the present invention is to provide a golf ball that is excellent in the flight performance, feel at impact and durability.

SUMMARY OF THE INVENTION

A golf ball according to one aspect of the present invention has a spherical core, amid layer positioned outside of this core, a reinforcing layer positioned outside of this mid layer, and a cover positioned outside of this reinforcing layer. This mid layer has a hardness Hm as measured with a Shore D type hardness scale of equal to or less than 54. Principal component of the base polymer of this cover is an ionomer resin. This cover has a hardness Hc as measured with a Shore D type hardness scale of equal to or greater than 55. This cover has a weight Wc of equal to or less than 5.7 g. This cover has a ratio (Wc/Hc) of the weight Wc to the hardness Hc of equal to or less than 0.080.

Preferably, the base polymer of the mid layer comprises 10% by weight or more and 60% by weight or less styrene block-containing thermoplastic elastomer, and 40% by weight or more and 90% by weight or less ionomer resin.

Preferably, the cover has a thickness Tc of equal to or less than 1.2 mm. Preferably, the mid layer has a thickness Tm of 0.5 mm or greater and 1.6 mm or less.

Preferably, the reinforcing layer comprises a water-based adhesive. Base polymer of this water-based adhesive is a reaction product between carboxyl group-containing polyurethane and polycarbodiimide. Preferably, the reinforcing layer has a thickness of 0.003 mm or greater and 0.050 mm or less.

A golf ball according to another aspect of the present invention has a spherical core, amid layer positioned outside of this core, a reinforcing layer positioned outside of this mid layer, and a cover positioned outside of this reinforcing layer. This mid layer has a thickness Tm of 0.5 mm or greater and 1.7 mm or less. Base polymer of this cover is an ionomer resin. The cover has a hardness Hc as measured with a Shore D type hardness scale of 56 or greater and 65 or less. This cover has a thickness Tc of equal to or less than 1.0 mm.

Preferably, the mid layer has a hardness Hm as measured with a Shore D type hardness scale of 30 or greater and 54 or less. Preferably, base polymer of this mid layer comprises 30% by weight or more and 60% by weight or less styrene block-containing thermoplastic elastomer, and 40% by weight or more and 70% by weight or less ionomer resin.

Preferably, base polymer of the reinforcing layer is a reaction product between carboxyl group-containing polyurethane and polycarbodiimide. Preferably, the carboxyl group-containing polyurethane and the polycarbodiimide are water-based.

In this golf ball, firm adhesion between the mid layer and the cover is permitted via the reinforcing layer. According to this golf ball, sufficient durability is achieved by virtue of the reinforcing layer even though a thin mid layer or a thin cover is employed. The thin mid layer can be responsible for resilience performance of the golf ball. The thin cover can be responsible for feel at impact of the golf ball. Also, the thin cover can optimize launch angle of the golf ball upon impact. This golf ball is excellent in the flight performance, feel at impact and durability.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a partially cut off cross-sectional view illustrating a golf ball according to one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is hereinafter described in detail with appropriate references to the accompanying drawing according to the preferred embodiments.

A golf ball 2 illustrated in FIG. 1 has a spherical core 4, a mid layer 6 covering this core 4, a reinforcing layer 8 covering this mid layer 6, and a cover 10 covering this reinforcing layer 8. Numerous dimples 12 are formed on the surface of the cover 10. Of the surface of the cover 10, a part except for the dimples 12 is a land 14. This golf ball 2 has a paint layer and a mark layer to the external side of the cover 10, although these layers are not shown in the FIGURE.

This golf ball 2 has a diameter of from 40 mm to 45 mm. From the standpoint of conformity to a rule defined by United States Golf Association (USGA), the diameter is preferably equal to or greater than 42.67 mm. In light of suppression of the air resistance, the diameter is preferably equal to or less than 44 mm, and more preferably equal to or less than 42.80 mm. Weight of this golf ball 2 is 40 g or greater and 50 g or less. In light of attainment of great inertia, the weight is preferably equal to or greater than 44 g, and more preferably equal to or greater than 45.00 g. From the standpoint of conformity to a rule defined by USGA, the weight is preferably equal to or less than 45.93 g.

The core 4 is usually obtained through crosslinking of a rubber composition. Illustrative examples of preferable base rubber include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers and natural rubbers. In light of the resilience performance, polybutadienes are preferred. When other rubber is used in combination with a polybutadiene, it is preferred that polybutadiene is included as a principal component. Specifically, it is preferred that percentage of polybutadiene occupying the entire base rubber is equal to or greater than 50% by weight, and particularly equal to or greater than 80% by weight. Polybutadienes having a percentage of cis-1,4 bonds of equal to or greater than 40%, and particularly equal to or greater than 80% are particularly preferred.

For crosslinking of the core 4, a co-crosslinking agent is usually used. Preferable examples of the co-crosslinking agent in light of the resilience performance include monovalent or bivalent metal salts of an α,β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Specific examples of preferable co-crosslinking agent include zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. Zinc acrylate and zinc methacrylate are particularly preferred on the grounds that a high resilience performance can be achieved.

As a co-crosslinking agent, an α,β-unsaturated carboxylic acid having 2 to 8 carbon atoms, and a metal oxide may be also blended. Both components react in the rubber composition to give a salt. This salt serves is responsible for the crosslinking reaction. Examples of preferable α,β-unsaturated carboxylic acid include acrylic acid and methacrylic acid. Examples of preferable metal oxide include zinc oxide and magnesium oxide.

In light of the resilience performance of the golf ball 2, the amount of the co-crosslinking agent to be blended is preferably equal to or greater than 10 parts by weight, and more preferably equal to or greater than 15 parts by weight per 100 parts by weight of the base rubber. In light of soft feel at impact, the amount of the co-crosslinking agent to be blended is preferably equal to or less than 50 parts by weight, and more preferably equal to or less than 45 parts by weight per 100 parts by weight of the base rubber.

Into the rubber composition for use in the core 4, an organic peroxide may be preferably blended together with the co-crosslinking agent. The organic peroxide serves as a crosslinking initiator. By blending the organic peroxide, the resilience performance of the golf ball 2 may be improved. Examples of suitable organic peroxide include dicumyl peroxide,

-   1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, -   2,5-dimethyl-2,5-di(t-butylperoxy)hexane and di-t-butyl peroxide.     Particularly versatile organic peroxide is dicumyl peroxide.

In light of the resilience performance of the golf ball 2, the amount of the organic peroxide to be blended is preferably equal to or greater than 0.1 part by weight, more preferably equal to or greater than 0.3 part by weight, and particularly preferably equal to or greater than 0.5 part by weight per 100 parts by weight of the base rubber. In light of soft feel at impact, the amount of the organic peroxide to be blended is preferably equal to or less than 3.0 parts by weight, and more preferably equal to or less than 2.5 parts by weight per 100 parts by weight of the base rubber.

Into the core 4 may be blended a filler for the purpose of adjusting specific gravity and the like. Illustrative examples of suitable filler include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. Powder of a highly dense metal may be blended as a filler. Specific examples of the highly dense metal include tungsten and molybdenum. The amount of the filler to be blended is determined ad libitum so that the intended specific gravity of the core 4 can be accomplished. Particularly preferable filler is zinc oxide. Zinc oxide serves not only to adjust the specific gravity but also as a crosslinking activator. Various kinds of additives such as sulfur, a sulfur compound, an anti-aging agent, a coloring agent, a plasticizer, a dispersant and the like may be blended at an adequate amount to the core 4 as needed. Into the core 4 may be also blended crosslinked rubber powder or synthetic resin powder.

It is preferred that the core 4 has a diameter of 30.0 mm or greater and 41.0 mm or less. Sufficient resilience performance of the golf ball 2 is achieved by setting the diameter to be equal to or greater than 30.0 mm. In this respect, the diameter is more preferably equal to or greater than 32.0 mm. Feel at impact by virtue of the mid layer 6 and the flight performance by virtue of the cover 10 can be achieved by setting the diameter to be equal to or less than 41.0 mm. In this respect, the diameter is more preferably equal to or less than 40.5 mm.

It is preferred that the core 4 has an amount of compressive deformation of 3.0 mm or greater and 6.0 mm or less. The core 4 having an amount of compressive deformation of equal to or greater than 3.0 mm is responsible for soft feel at impact. In this respect, the amount of compressive deformation is more preferably equal to or greater than 3.4 mm. The core 4 having an amount of compressive deformation of equal to or less than 6.0 mm is responsible for the resilience performance of the golf ball 2. In this respect, the amount of compressive deformation is more preferably equal to or less than 5.5 mm.

Upon measurement of the amount of compressive deformation, the core 4 is first placed on a hard plate made of metal. Next, a cylinder made of metal gradually descends toward the core 4. The core 4 intervened between the bottom face of the cylinder and the hard plate is deformed. A migration distance of the cylinder, starting from the state in which initial load of 98 N is applied to the core 4 up to the state in which final load of 1274 N is applied thereto is the amount of compressive deformation.

Weight of the core 4 is preferably 25 g or greater and 42 g or less. Crosslinking temperature of the core 4 is usually 140° C. or greater and 180° C. or less. The crosslinking time period of the core 4 is usually 10 minutes or longer and 60 minutes or less. The core 4 may be formed with two or more layers. Other layer comprising a resin composition or a rubber composition may be provided between the core 4 and the mid layer 6.

Base polymer of the mid layer 6 comprises a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer is responsible for the feel at impact of the golf ball 2. In light of the feel at impact, it is preferred that proportion of the styrene block-containing thermoplastic elastomer to total amount of the base polymer is equal to or greater than 10% by weight, yet equal to or greater than 25% by weight, still equal to or greater than 30% by weight, and further equal to or greater than 40% by weight.

Examples of the styrene block-containing thermoplastic elastomer include styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene block copolymers (SIS), styrene-isoprene-butadiene-styrene block copolymers (SIBS), hydrogenated SBS, hydrogenated SIS and hydrogenated SIBS. Exemplary hydrogenated SBS may include styrene-ethylene-butylene-styrene block copolymers (SEGS). Exemplary hydrogenated SIS may include styrene-ethylene-propylene-styrene block copolymers (SEPS). Exemplary hydrogenated SIBS may include styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS).

In the present invention, exemplary styrene block-containing thermoplastic elastomer may include alloys of olefin and one or two or more selected from the group consisting of SBS, SIS, SIBS, SEGS, SEPS and SEEPS, and hydrogenated products thereof. Olefin component in these alloys is presumed to be responsible for the improvement of compatibility between the thermoplastic elastomer and the ionomer resin. Use of this alloy may improve the resilience performance of the golf ball 2. Preferably, an olefin having 2 to 10 carbon atoms may be used.

In light of the resilience performance of the golf ball 2, content of the styrene component in the thermoplastic elastomer is preferably equal to or greater than 10% by weight, more preferably equal to or greater than 12% by weight, and particularly preferably equal to or greater than 15% by weight. In light of the feel at impact of the golf ball 2, the content is preferably equal to or less than 50% by weight, more preferably equal to or less than 47% by weight, and particularly preferably equal to or less than 45% by weight.

Specific examples of the styrene block-containing thermoplastic elastomer include “Rabalon® T3339C”, “Rabalon® SJ5400N”, “Rabalon® SJ6400N”, “Rabalon® SJ7400N”, “Rabalon® SJ8400N”, “Rabalon® SJ9400N” and “Rabalon® SR04”, trade names by Mitsubishi Chemical Corporation; “Epofriend® A1010”, a trade name by Daicel Chemical Industries; and “Septon HG-252”, a trade name by Kuraray Co., Ltd.

The base polymer of the mid layer 6 comprises an ionomer resin together with the styrene block-containing thermoplastic elastomer. Ionomer resins are highly elastic. The ionomer resin is responsible for the resilience performance of the golf ball 2. In light of the resilience performance, proportion of the ionomer resin to total amount of the base polymer is preferably equal to or greater than 40% by weight, and more preferably equal to or greater than 50% by weight.

Examples of preferred ionomer resin include binary copolymers formed with α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Examples of the other ionomer resin include ternary copolymers formed with α-olefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α,β-unsaturated carboxylate ester having 2 to 22 carbon atoms. In the binary copolymer and ternary copolymer, preferable α-olefin may be ethylene and propylene, while preferable α,β-unsaturated carboxylic acid may be acrylic acid and methacrylic acid. In the binary copolymer and ternary copolymer, a part of the carboxyl group may be neutralized with a metal ion. Illustrative examples of the metal ion for use in neutralization include sodium ion, potassium ion, lithium ion, zinc ion, calcium ion, magnesium ion, aluminum ion and neodymium ion. The neutralization may be carried out with two or more kinds of metal ions. Particularly suitable metal ion in light of the resilience performance and durability of the golf ball 2 is sodium ion, zinc ion, lithium ion and magnesium ion.

Preferable binary copolymer comprises 80% by weight or more and 90% by weight or less α-olefin, and 10% by weight or more and 20% by weight or less α,β-unsaturated carboxylic acid. This binary copolymer provides excellent resilience performance. Preferable ternary copolymer comprises 70% by weight or more and 85% by weight or less α-olefin, 5% by weight or more and 30% by weight or less α,β-unsaturated carboxylic acid, and 1% by weight or more and 25% by weight or less α,β-unsaturated carboxylate ester. This ternary copolymer provides excellent resilience performance.

Particularly preferred ionomer resin is a copolymer formed with ethylene, and acrylic acid or methacrylic acid. Preferably, this ionomer resin has a melt index of 3 or greater and 7 or less. This ionomer resin exhibits superior fluidity. Preferably, this ionomer resin has a flexural rigidity of 200 MPa or greater and 400 MPa or less. This ionomer resin is highly elastic.

Specific examples of the ionomer resin include trade names “Himilan 1555”, “Himilan 1557”, “Himilan 1605”, “Himilan 1706”, “Himilan 1707”, “Himilan AM7311”, “Himilan AM7315”, “Himilan AM7317”, “Himilan AM7318” and “Himilan MK7320”, available from Du Pont-MITSUI POLYCHEMICALS Co., Ltd.; trade names; “Surlyn® 7930”, “Surlyn® 7940”, “Surlyn® 8140”, “Surlyn® 8940”, “Surlyn® 8945”, “Surlyn® 9120”, “Surlyn® 9910” and “Surlyn® 9945”, available from Dupont; and trade names “IOTEK 7010”, “IOTEK 7030”, “IOTEK 8000” and “IOTEK 8030”, available from EXXON Corporation. Two or more kinds of the ionomer resin may be used in combination. An ionomer resin neutralized with a monovalent metal ion, and an ionomer resin neutralized with a bivalent metal ion may be used in combination.

Other resin may be also used in the mid layer 6 together with the styrene block-containing thermoplastic elastomer and the ionomer resin. Illustrative examples of the other resin include thermoplastic polyester elastomers, thermoplastic polyamide elastomers, thermoplastic polyurethane elastomers and thermoplastic polyolefin elastomers.

Into the resin composition of the mid layer 6 may be blended a filler for the purpose of adjusting specific gravity and the like. Illustrative examples of suitable filler include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. Powder of a highly dense metal may be also blended as a filler. Specific examples of the highly dense metal include tungsten and molybdenum. The amount of the filler to be blended is determined ad libitum so that intended specific gravity of the mid layer 6 can be accomplished. Into the mid layer 6 may be also blended a coloring agent, crosslinked rubber powder or synthetic resin powder.

It is preferred that the mid layer 6 has a hardness Hm of equal to or less than 54. The mid layer 6 having a hardness Hm of equal to or less than 54 may be responsible for soft feel at impact. In this respect, the hardness Hm may be equal to or less than 53, more preferably equal to or less than 52, still preferably equal to or less than 51, and further preferably equal to or less than 48. In light of the resilience performance of the golf ball 2, the hardness Hm is preferably equal to or greater than 30, more preferably equal to or greater than 33, still more preferably equal to or greater than 34, and further preferably equal to or greater than 37.

In the present invention, the hardness Hm of the mid layer 6 and the hardness Hc of the cover 10 may be measured in accordance with a standard of “ASTM-D 2240-68”. For the measurement, an automated rubber hardness scale (trade name “P1”, available from Koubunshi Keiki Co., Ltd.) which is equipped with a Shore D type spring hardness scale is used. For the measurement, a sheet which was formed by hot press is used having a thickness of about 2 mm and consisting of the same material as the mid layer 6 (or the cover 10). Prior to the measurement, the sheet is stored at a temperature of 23° C. for two weeks. When the measurement is carried out, three sheets are overlaid.

The mid layer 6 has a thickness Tm of preferably 0.5 mm or greater and 1.6 mm or less. The mid layer 6 having the thickness Tm of equal to or greater than 0.5 mm may be responsible for soft feel at impact. In this respect, the thickness Tm is more preferably equal to or greater than 0.6 mm. By setting the thickness Tm to be equal to or less than 1.6 mm, adverse effects of the mid layer 6 on the resilience performance can be suppressed. In this respect, the thickness Tm is more preferably equal to or less than 1.5 mm, and particularly preferably equal to or less than 1.2 mm.

The surface of the mid layer 6 may be subjected to a treatment such as brushing, grinding or the like. This treatment can increase the roughness of the surface. Great roughness improves adhesion between the mid layer 6 and the reinforcing layer 8 or the cover 10.

The reinforcing layer 8 lies between the mid layer 6 and the cover 10. The reinforcing layer 8 adheres firmly to the mid layer 6, and adheres firmly also to the cover 10. As described above, this golf ball 2 has a thin mid layer 6. As described later, this golf ball 2 has an extremely thin cover 10. Because the cover 10 adheres firmly to the mid layer 6 via the reinforcing layer 8, the mid layer 6 and the cover 10 are not easily broken irrespective of the mid layer 6 and the cover 10 being thin. This golf ball 2 is excellent in durability. In other words, the presence of the reinforcing layer 8 permits to provide the thin mid layer 6 and thin cover 10.

Preferably, base polymer of the reinforcing layer 8 is a reaction product between carboxyl group-containing polyurethane and polycarbodiimide. This reinforcing layer 8 has a three-dimensional structure, and is excellent in the strength. Moreover, this reinforcing layer 8 is excellent in adhesiveness to the mid layer 6 and adhesiveness to the cover 10.

The reinforcing layer 8 preferably comprises a water-based adhesive. The water-based adhesive is excellent in workability, and does not adversely affect the environment. In particular, it is preferably a reaction product between water-based carboxyl group-containing polyurethane and water-based polycarbodiimide. A liquid obtained by mixing an aqueous solution or a water dispersion liquid of carboxyl group-containing polyurethane with an aqueous solution or a water dispersion liquid of polycarbodiimide is applied on the mid layer 6 to obtain the reinforcing layer 8 through a reaction of the carboxyl group-containing polyurethane with the polycarbodiimide.

Anionic or nonionic carboxyl group-containing polyurethane liquid can be used. In the anionic carboxyl group-containing polyurethane liquid, the polyurethane is dissolved or dispersed in water through neutralization of the carboxyl group with a base. In the nonionic carboxyl group-containing polyurethane liquid, the polyurethane is dispersed forcedly in water with a high shearing force in the presence of a nonionic emulsifying agent.

Polyisocyanate component in the carboxyl group-containing polyurethane has multiple isocyanate groups. Specific examples of the polyisocyanate include aromatic polyisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, mixtures of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI) and paraphenylene diisocyanate (PPDI); alicyclic polyisocyanates such as 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenated xylylene diisocyanate (H₆XDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI); and aliphatic polyisocyanates. Two or more polyisocyanates may be used in combination. In light of the weather resistance, TMXDI, XDI, HDI, H₆XDI, IPDI and H₁₂MDI are preferred.

Polyol component in the carboxyl group-containing polyurethane has multiple hydroxyl groups. A low molecular weight polyol having a molecular weight of less than 500 and a high molecular weight polyol having a molecular weight of equal to or greater than 500 can be used. Examples of the low molecular weight polyol include diol and triol. Specific examples of the diol include ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol and 1,6-hexanediol. Specific examples of the triol include glycerin, trimethylolpropane and hexanetriol. Examples of the high molecular weight polyol include polyether polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG) and polyoxytetramethylene glycol (PTMG); condensed polyester polyols such as polyethylene adipate (PEA), polybutylene adipate (PBA) and polyhexamethylene adipate (PHMA); lactone based polyester polyols such as poly-ε-caprolactone (PCL); polycarbonate polyols such as polyhexamethylene carbonate; and acrylic polyols. Two or more kinds of polyols may be used in combination. Polyols having a weight average molecular weight of 50 or greater and 2000 or less, particularly 100 or greater and 1000 or less are particularly preferred.

The carboxyl group-containing polyurethane may contain a polyamine component. Examples of the polyamine component include aliphatic polyamines such as ethylenediamine, propylenediamine and hexamethylenediamine; aromatic polyamines such as tolylenediamine, xylylenediamine and diaminodiphenylmethane; alicyclic polyamines such as diaminocyclohexylmethane, piperazine and isophoronediamine; and hydrazines such as hydrazine, succinic acid dihydrazide, adipic acid dihydrazide and phthalic acid dihydrazide. Alkanolamines such as diethanolamine and monoethanolamine may be used.

The water-based polycarbodiimide has two or more carbodiimide groups within the molecule, and is thus soluble or dispersible in water. Suitably, a polycarbodiimide resin having a structure represented by the following formula (I) may be used.

S1-K-(R—N═C═N)_(n)—R-K-S2  (I)

In the above formula (I), S1 and S2 represent a hydrophilic segment; R represents a residue yielded by excluding the isocyanate group from diisocyanate; K represents a bond formed by a reaction of the isocyanate group with the hydrophilic segment; and n represents an average degree of polymerization. The symbol n represents an integer of 2 or greater and 100 or less. Illustrative examples of the hydrophilic segment include nonionic segments having an ethyleneoxide chain; anionic segments having a sulfonate salt, a sulfate salt or the like; and cationic segments having a quaternary ammonium salt. Specific examples of the polycarbodiimide resin represented by the above formula (I) include tetramethylxylylenecarbodiimide and dicyclohexylmethanecarbodiimide.

Carbodiimide equivalent in the water-based polycarbodiimide is preferably 100 or greater and 500 or less. By setting the carbodiimide equivalent to be equal to or greater than 100, the reinforcing layer 8 having great crosslinking density is obtained. This reinforcing layer 8 is responsible for adhesion between the mid layer 6 and the cover 10. In this respect, the carbodiimide equivalent is more preferably equal to or greater than 150, and particularly preferably equal to or greater than 250. By using the polycarbodiimide having the carbodiimide equivalent of equal to or less than 500, the reaction with the carboxyl group-containing polyurethane can be completed in a short period of time. In this respect, the carbodiimide equivalent is more preferably equal to or less than 450, and particularly preferably equal to or less than 400. The carbodiimide equivalent refers to the chemical formula weight of polycarbodiimide per mol of the carbodiimide group.

Solid content of the polycarbodiimide in the aqueous solution or the water dispersion liquid is preferably equal to or greater than 20% by weight, and more preferably equal to or greater than 30% by weight. The solid content is preferably equal to or less than 80% by weight, and more preferably equal to or less than 70% by weight. Illustrative examples of preferable aqueous solution of polycarbodiimide include trade names of “Carbodilite® E-01”, “Carbodilite® E-02” and “Carbodilite® E-03A”, available from Nisshin Spinning Co., Ltd.

Amount of the polycarbodiimide to be blended is preferably parts by weight or greater and 25 parts by weight or less per 100 parts by weight of the carboxyl group-containing polyurethane. By setting the amount to be equal to or greater than 5 parts by weight, a reinforcing layer 8 having great crosslinking density may be obtained. This reinforcing layer 8 is responsible for adhesion between the mid layer 6 and the cover 10. In this respect, the amount is more preferably equal to or greater than 6 parts by weight, and particularly preferably equal to or greater than 7 parts by weight. By setting the amount to be equal to or less than 25 parts by weight, the reaction with the carboxyl group-containing polyurethane can be completed in a short period of time. In this respect, the amount is more preferably equal to or less than 23 parts by weight, and particularly preferably equal to or less than 20 parts by weight.

The reinforcing layer 8 may comprise an oil-based adhesive. As the base polymer of this reinforcing layer 8, a two-component cured thermosetting resin may be typically used. Specific examples of the two-component cured thermosetting resin include epoxy resins, urethane resins, acrylic resins, polyester based resins and cellulose based resins. In light of the mechanical characteristics (e.g., strength at break) and durability of the reinforcing layer 8, two-component cured epoxy resins and two-component cured urethane resins are preferred.

The two-component cured epoxy resin is obtained by curing an epoxy resin with a polyamide based curing agent. Illustrative examples of the epoxy resin for use in the two-component cured epoxy resin include bisphenol A type epoxy resins, bisphenol F type epoxy resins and bisphenol AD type epoxy resins. The bisphenol A type epoxy resin is obtained by a reaction of bisphenol A with an epoxy group-containing compound such as epichlorohydrin. The bisphenol F type epoxy resin is obtained by a reaction of bisphenol F with an epoxy group-containing compound. The bisphenol AD type epoxy resin is obtained by a reaction of bisphenol AD with an epoxy group-containing compound. In light of the balance among softness, chemical resistance, heat resistance and toughness, the bisphenol A type epoxy resins are preferred.

The polyamide based curing agent has multiple amino groups and one or more amide groups. This amino group can react with an epoxy group. Specific examples of the polyamide based curing agent include polyamide amine curing agents and modified products of the same. The polyamide amine curing agent is obtained by a condensation reaction of a polymerized fatty acid with a polyamine. Typical polymerized fatty acid may be obtained by heating naturally occurring fatty acids containing large amounts of unsaturated fatty acids such as linoleic acid, linolenic acid and the like in the presence of a catalyst to perfect the synthesis. Specific examples of the unsaturated fatty acid include tall oil, soybean oil, linseed oil and fish oil. Polymerized fatty acids having a dimer content of equal to or greater than 90% by weight and a trimer content of equal to or less than 10% by weight, and being hydrogenated are preferred. Illustrative examples of preferred polyamine include polyethylenediamine, polyoxyalkylenediamine and derivatives thereof.

Upon mixing of the epoxy resin and the polyamide based curing agent, ratio of epoxy equivalent of the epoxy resin and amine active hydrogen equivalent of the polyamide based curing agent is preferably 1.0/1.4 or greater and 1.0/1.0 or less.

The two-component cured urethane resin is obtained by a reaction of a base material and a curing agent. A two-component cured urethane resin obtained by a reaction of a base material containing a polyol component with a curing agent containing polyisocyanate or a derivative thereof, or a two-component cured urethane resin obtained by a reaction of a base material containing isocyanate group-ended urethane prepolymer with a curing agent having an active hydrogen may be used. In particular, two-component cured urethane resins obtained by a reaction of a base material containing a polyol component with a curing agent containing polyisocyanate or a derivative thereof are preferred.

It is preferred that an urethane polyol is used as the polyol component of the base material. The urethane polyol has urethane bonds and two or more hydroxyl groups. Preferably, the urethane polyol has a hydroxyl group at its end. The urethane polyol may be obtained by allowing a polyol and a polyisocyanate to react at a ratio such that an excessive molar ratio of the hydroxyl group of the polyol component to the isocyanate group of polyisocyanate is attained.

The polyol for use in production of the urethane polyol has multiple hydroxyl groups. Polyol having a weight average molecular weight of 50 or greater and 2000 or less, and particularly 100 or greater and 1000 or less is preferred. Examples of the polyol having a low molecular weight include diol and triol. Specific examples of the diol include ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol and 1,6-hexanediol. Specific examples of the triol include trimethylolpropane and hexanetriol. Examples of the polyol having a high molecular weight include polyether polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG) and polyoxytetramethylene glycol (PTMG); condensed polyester polyols such as polyethylene adipate (PEA), polybutylene adipate (PBA) and polyhexamethylene adipate (PHMA); lactone based polyester polyols such as poly-ε-caprolactone (PCL); polycarbonate polyols such as polyhexamethylene carbonate; and acrylic polyols. Two or more kinds of polyols may be used in combination.

Polyisocyanate for use in production of the urethane polyol has multiple isocyanate groups. Specific examples of the polyisocyanate include aromatic polyisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, mixtures of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI) and paraphenylene diisocyanate (PPDI); alicyclic polyisocyanates such as 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenated xylylene diisocyanate (H₆XDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI); and aliphatic polyisocyanates. Two or more polyisocyanates may be used in combination. In light of the weather resistance, TMXDI, XDI, HDI, H₆XDI, IPDI and H₁₂MDI are preferred.

In the reaction of the polyol with the polyisocyanate for producing the urethane polyol, any known catalyst may be used. Typical catalyst may be dibutyltin dilaurate.

In light of strength of the reinforcing layer 8, proportion of urethane bonds included in the urethane polyol is preferably equal to or greater than 0.1 mmol/g. In light of the following capability of the reinforcing layer 8 to the cover 10, the proportion of urethane bonds included in the urethane polyol is preferably equal to or less than 5 mmol/g. The proportion of urethane bonds may be adjusted by regulating the molecular weight of the polyol to be a raw material, and by regulating compounding ratio of the polyol and the polyisocyanate.

In light of a short time period required for the reaction of the base material with the curing agent, the urethane polyol has a weight average molecular weight of preferably equal to or greater than 4000, and more preferably equal to or greater than 4500. In light of adhesiveness of the reinforcing layer 8, the urethane polyol has a weight average molecular weight of preferably equal to or less than 10000, and more preferably equal to or less than 9000.

In light of adhesiveness of the reinforcing layer 8, the urethane polyol has a hydroxyl value (mgKOH/g) of preferably equal to or greater than 15, and more preferably equal to or greater than 73. In light of a short time period required for the reaction of the base material with the curing agent, the urethane polyol has a hydroxyl value of preferably equal to or less than 130, and more preferably equal to or less than 120.

The base material may contain, in addition to the urethane polyol, a polyol not having any urethane bond. The aforementioned polyol that may be a raw material of the urethane polyol can be used in the base material. Polyols that are compatible with the urethane polyol are preferred. In light of a short time period required for the reaction of the base material with the curing agent, proportion of the urethane polyol in the base material is preferably equal to or greater than 50% by weight, and more preferably equal to or greater than 80% by weight based on the solid content. Ideally, this proportion is 100% by weight.

The curing agent contains polyisocyanate or a derivative thereof. The aforementioned polyisocyanate that is a raw material of the urethane polyol may be used as the curing agent.

The reinforcing layer 8 comprises the two-component cured thermosetting resin is obtained by applying a liquid prepared by dissolving or dispersing the base material and the curing agent in a solvent on the surface of the mid layer 6. In light of the workability, application with a spray gun is preferred. Following the application, the solvent is volatilized to permit a reaction of the base material with the curing agent thereby forming the reinforcing layer 8. Illustrative examples of preferred solvent include toluene, isopropyl alcohol, xylene, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether, ethylbenzene, propylene glycol monomethyl ether, isobutyl alcohol and ethyl acetate.

In light of the durability of the golf ball 2, the reinforcing layer 8 has a thickness of preferably equal to or greater than 0.003 mm, and more preferably equal to or greater than 0.005 mm. In light of easy formation of the reinforcing layer 8, it is preferred that the thickness is equal to or less than 0.30 mm, still more, equal to or less than 0.10 mm, yet more, equal to or less than 0.05 mm, and furthermore, equal to or less than 0.02 mm. The thickness is measured by observation of the cross section of the golf ball 2 with a micro scope. When the surface of the mid layer 6 has roughness resulting from the surface roughening treatment, the thickness is measured immediately above the protruded portion.

Principal component of the base polymer of the cover 10 is an ionomer resin. The aforementioned binary copolymer ionomer resin and the ternary copolymer ionomer resin can be used in the cover 10. The ionomer resin is highly elastic. By using the ionomer resin in the cover 10, a golf ball 2 that is excellent in resilience performance is obtained.

As described above, the mid layer 6 comprises a styrene block-containing thermoplastic elastomer. When this mid layer 6 and the cover 10 comprising the ionomer resin are directly attached, adhesiveness therebetween may become insufficient. In the present golf ball 2, the reinforcing layer 8 lies between the mid layer 6 and the cover 10, therefore, firm adhesion between the mid layer 6 and the cover 10 is permitted via this reinforcing layer 8.

Other resin may be used in the cover 10 together with the ionomer resin. Examples of the other resin include styrene block-containing thermoplastic elastomers, thermoplastic polyurethane elastomers, thermoplastic polyester elastomers, thermoplastic polyamide elastomers and thermoplastic polyolefin elastomers. When the other resin is used in combination with the ionomer resin, proportion of the ionomer resin in total amount of the base polymer is preferably equal to or greater than 50% by weight, and more preferably equal to or greater than 70% by weight, and particularly preferably equal to or greater than 90% by weight.

Into the cover 10 may be blended a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorbent, a light stabilizer, a fluorescent agent, a fluorescent brightening agent and the like in an appropriate amount as needed. Powder of a highly dense metal such as tungsten, molybdenum or the like may be also blended into the cover 10 for the purpose of adjusting the specific gravity.

The cover 10 has a hardness Hc of equal to or greater than 55. The cover 10 having a hardness Hc of equal to or greater than 55 is responsible for the resilience performance. In this respect, the hardness Hc is preferably equal to or greater than 56, more preferably equal to or greater than 57, and still more preferably equal to or greater than 58. In light of soft feel at impact, the hardness Hc is preferably equal to or less than 65, more preferably equal to or less than 64, and still more preferably equal to or less than 63.

The cover 10 has a thickness Tc of equal to or less than 1.2 mm. This cover 10 is extremely thin. By employing such a thin cover 10, a great launch angle can be accomplished upon impact with a golf club. The great launch angle is responsible for great flight distance. Moreover, by employing a thin cover 10, adverse effects of the cover 10 on the feel at impact can be suppressed. In this respect, the thickness Tc is preferably equal to or less than 1.0 mm, more preferably equal to or less than 0.9 mm, still more preferably equal to or less than 0.8 mm, and even more preferably equal to or less than 0.5 mm. Although the thin cover 10 is apt to be broken upon repeated impacts, the reinforcing layer 8 suppresses the breakage in this golf ball 2. This golf ball 2 is excellent in the flight performance, feel at impact and durability. In light of ease of production, the cover 10 has a thickness Tc of equal to or greater than 0.1 mm, and more preferably equal to or greater than 0.3 mm. The thickness Tc is measured immediately below the land 14 where no dimple 12 exists.

The cover 10 has a weight Wc of equal to or less than 5.7 g. By setting the weight Wc to be equal to or less than 5.7 g, a great launch angle can be provided. The great launch angle is responsible for great flight distance. Furthermore, by setting the weight Wc to be equal to or less than 5.7 g, adverse effect on the feel at impact exerted by the cover 10 may be suppressed. In this respect, the weight Wc is more preferably equal to or less than 5.3 g, and particularly preferably equal to or less than 4.8 g. In light of ease of production, the cover 10 has a weight Wc of preferably equal to or greater than 1.5 g, more preferably equal to or greater than 1.7 g, and particularly preferably equal to or greater than 1.9 g.

Ratio (Wc/Hc) of the weight Wc to the hardness Hc in the cover 10 is equal to or less than 0.080. By setting the ratio (Wc/Hc) to be equal to or less than 0.080, great launch angle and great resilience coefficient can be both achieved simultaneously. In this respect, the ration (Wc/Hc) is more preferably equal to or less than 0.078, and particularly preferably equal to or less than 0.075. The ratio (Wc/Hc) is preferably equal to or greater than 0.030. By setting the ratio (Wc/Hc) to be equal to or greater than 0.030, productivity and feel at impact can be both achieved simultaneously. The ratio (Wc/Hc) is an index that represents the degree of contribution of the cover 10 to the launch angle, resilience coefficient, productivity and feel at impact of the golf ball 2.

Amount of compressive deformation of the golf ball 2 is preferably 2.0 mm or greater and 4.5 mm or less. The golf ball 2 having the amount of compressive deformation of equal to or greater than 2.0 mm is excellent in the feel at impact. In this respect, the amount of compressive deformation is more preferably equal to or greater than 2.2 mm, and particularly preferably equal to or greater than 2.3 mm. The golf ball 2 having the amount of compressive deformation of equal to or less than 4.5 mm is excellent in the resilience performance. In this respect, the amount of compressive deformation is more preferably equal to or less than 4.3 mm, and particularly preferably equal to or less than 4.0 mm. The amount of compressive deformation of the golf ball 2 is measured in accordance with the method for measuring the amount of compressive deformation of the core 4 as described above.

EXAMPLES Experiment 1 Example 1

A type x rubber composition was obtained by kneading 100 parts by weight of high cis-polybutadiene (trade name “BR-730”, available from JSR Corporation), 25 parts by weight of zinc acrylate, 10 parts of zinc oxide, an adequate amount of barium sulfate, 0.5 part by weight of diphenyl disulfide (manufactured by Sumitomo Seika Chemicals Co., Ltd.) and 0.8 part by weight of dicumyl peroxide (manufactured by NOF Corporation). This rubber composition was placed into a mold having upper and lower mold half each having a hemispherical cavity, and heated at 170° C. for 20 minutes to obtain a core having a diameter of 39.2 mm.

In a biaxial extruder having a screw diameter of 45 mm, which provides a rotational velocity of the screw being 200 rpm, and having L/D of 35, a type b resin composition shown in Table 1 below was obtained. Temperature in the die during extrusion of the resin composition was from 180° C. to 230° C. The core was covered by this resin composition therearound with injection molding to obtain a mid layer. This mid layer had a thickness Tm of 1.0 mm, and a hardness Hm of 42.

An aqueous solution of carboxyl group-containing polyurethane (trade name “W-615”, available from Mitsui Takeda Chemicals, Inc.) in an amount of 100 parts by weight was mixed with 10 parts by weight of a water dispersion liquid of polycarbodiimide (trade name “Carbodilite® E-03A”, supra). This aqueous solution of carboxyl group-containing polyurethane had an acid value of 9 mg KOH/g, and a solid content of 35% by weight. This water dispersion liquid of polycarbodiimide had a carbodiimide equivalent of 365, and a solid content of 40% by weight. This mixture was applied on the mid layer by a spray gun to obtain a reinforcing layer having a thickness of 0.008 mm.

A type e resin composition shown in Table 2 below was obtained in the aforementioned biaxial extruder. Half shell was obtained from this resin composition with compression molding. The spherical body composed of the core, the mid layer and the reinforcing layer was covered by two pieces of the half shell, and placed into a mold having upper and lower mold half each having a hemispherical cavity to obtain a cover by compression molding. The cover had a thickness Tc of 0.8 mm. A paint layer was formed around this cover to give a golf ball of Example 1. This golf ball had a diameter of 42.8 mm.

Examples 3 to 4

In a similar manner to Example 1 except that the diameter of the core and the thickness of the mid layer were as listed in Table 3 below, golf balls of Examples 3 to 4 were obtained.

Examples 2, 5 and 6, and Comparative Example 1

In a similar manner to Example 1 except that the type of the resin composition of the mid layer was as listed in Table 3 below, golf balls of Examples 2, 5 and 6, and Comparative Example 1 were obtained. Details of the resin composition are shown in Table 2 below.

Comparative Example 2

In a similar manner to Example 1 except that the type of the resin composition of the cover was as listed in Table 4 below, golf ball of Comparative Example 2 was obtained. Details of the resin composition are shown in Table 2 below.

Examples 7 to 8 and Comparative Example 3

In a similar manner to Example 1 except that the diameter of the core and the thickness of the cover were as listed in Table 4 below, golf balls of Examples 7 to 8 were obtained. In a similar manner to Example 1 except that the type of the rubber composition and the diameter of the core, and the thickness of the cover were as listed in Table 4 below, golf ball of Comparative Example 3 was obtained. Details of the rubber composition are shown in Table 1 below.

Example 9

In a similar manner to Example 1 except that a coating composition comprising a two-component cured epoxy resin as the base polymer (trade name “POLIN 750LE”, available from Shinto Paint Co., Ltd.) was used for forming the reinforcing layer, golf ball of Example 9 was obtained. This coating composition was prepared by mixing 100 parts by weight of the base material with 100 parts by weight of the curing agent. This base material contains a 30% by weight bisphenol A type epoxy resin and a 70% by weight solvent. This curing agent contains 40% by weight modified polyamide amine, 5% by weight titanium dioxide, and a 55% by weight solvent.

Comparative Example 4

In a similar manner to Example 1 except that the reinforcing layer was not provided, golf ball of Comparative Example 4 was obtained.

Examples 10 to 11

In a similar manner to Example 1 except that specifications of the core, the mid layer and the cover were as listed in Table 4 below, golf balls of Examples 10 to 11 were obtained.

[Measurement of Amount of Compressive Deformation]

In a similar manner to the measurement of the amount of compressive deformation of the core described above, amount of compressive deformation of the golf ball was measured. The results are shown in Table 3 and Table 4 below.

[Evaluation of Durability]

A driver with a metal head was attached to a swing machine available from True Temper Co. Then the machine condition was set to give the head speed of 45 m/sec, and the golf balls were hit therewith to allow for impact on a plate for impact. Accordingly, the number of times of the hitting until the golf ball was broken was counted. Mean values of the measurement of six golf balls were determined. The results are shown in Table 3 and Table 4 below in terms of indices on the basis of the value in Comparative Example 4 being presumed as 100.

[Measurement of Flight Distance]

A driver with a metal head was attached to the swing machine described above. Then the machine condition was set to give the head speed of 45 m/sec, and the golf balls were hit therewith. Accordingly, the distance from the launching point to the point where the ball stopped was measured. Mean values of 10 times measurement are shown in Table 3 and Table 4 below.

[Evaluation of Feel at Impact]

Using a driver, the golf balls were hit by a golf player, and the feel at impact was rated among the following four ranks of from “A” to “D”.

A: extremely favorable

B: favorable

C: somewhat unfavorable

D: unfavorable.

The results are presented in Table 3 and Table 4 below.

TABLE 1 Rubber composition of core (part by weight) Type x y BR-730 100 100 Zinc acrylate 25 24 Zinc oxide 10 10 Barium sulfate adequate amount adequate amount Diphenyl disulfide 0.5 0.5 Dicumyl peroxide 0.8 0.8

TABLE 2 Resin compositions of mid layer and cover (part by weight) Type a b c d e f g Surlyn 8945 20 26 37 40 45 50 — Surlyn 9945 20 26 37 40 45 50 — Rabalon SR04 60 48 26 20 10 — — Elastollan XNY97A* — — — — — — 100 Titanium dioxide 4.0 4.0 4.0 4.0 4.0 4.0 4.0 Ultra Marine Blue 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Hardness (Shore D) 30 42 53 56 60 63 42 *Thermoplastic polyurethane elastomer, available from BASF Co., Ltd.

TABLE 3 Results of evaluation Compara. Example 2 Example 3 Example 1 Example 4 Example 5 Example 6 Example 1 Core Type x x x x x x x Diameter (mm) 39.2 39.8 39.2 38.8 39.2 39.2 39.2 Mid Type a b b b g c d layer Hardness Hm 30 42 42 42 42 53 56 (Shore D) Thickness Tm (mm) 1.0 0.7 1.0 1.2 1.0 1.0 1.0 Reinforcing Base Polymer water- water- water- water- water- water- water- layer based based based based based based based urethane urethane urethane urethane urethane urethane urethane Cover Type e e e e e e e Hardness Hc 60 60 60 60 60 60 60 (Shore D) Thickness Tc (mm) 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Weight Wc (g) 4.0 4.0 4.0 4.0 4.0 4.0 4.0 Wc/Hc 0.067 0.067 0.067 0.067 0.067 0.067 0.067 Amount of compressive 3.6 3.4 3.5 3.6 3.5 3.5 3.3 deformation (mm) of ball Durability 140 143 143 144 134 144 144 Travel distance (m) 252 259 257 256 252 256 255 Feel at impact A A A A B B C

TABLE 4 Results of evaluation Compara. Compara. Compara. Example Example Example 2 Example 7 Example 8 Example 3 Example 9 Example 4 10 11 Core Type x x x y x x x x Diameter (mm) 39.2 39.8 38.8 38.0 39.2 39.2 38.8 40.4 Mid Type b b b b b b b b layer Hardness Hm 42 42 42 42 42 42 42 42 (Shore D) Thickness Tm (mm) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.7 Reinforcing Base polymer water- water- water- water- epoxy — water- water- layer based based based based based based urethane urethane urethane urethane urethane urethane Cover Type c e e e e e f e Hardness Hc 53 60 60 60 60 60 63 60 (Shore D) Thickness Tc (mm) 0.8 0.5 1.0 1.4 0.8 0.8 1.0 0.5 Weight Wc (g) 4.0 2.5 4.7 6.3 4.0 4.0 4.7 2.5 Wc/Hc 0.075 0.042 0.075 0.105 0.067 0.067 0.075 0.042 Amount of compressive 3.6 3.6 3.5 3.4 3.5 3.5 3.4 3.7 deformation (mm) of ball Durability 145 142 142 142 142 100 142 130 Travel distance (m) 240 259 256 242 257 248 256 260 Feel at impact B A A B A A A A

As is clear from Table 3 and Table 4, the golf balls of Examples are excellent in all terms of the durability, flight performance and feel at impact. Therefore, advantages of the present invention are clearly suggested by these results of evaluation.

Experiment 2 Example 12

A type x rubber composition shown in Table 1 above was obtained by kneading 100 parts by weight of high cis-polybutadiene (trade name “BR-730”, available from JSR Corporation), 25 parts by weight of zinc acrylate, 10 parts of zinc oxide, an adequate amount of barium sulfate, 0.5 part by weight of diphenyl disulfide and 0.8 part by weight of dicumyl peroxide. This rubber composition was placed into a mold having upper and lower mold half each having a hemispherical cavity, and heated at 170° C. for 20 minutes to obtain a core having a diameter of 38.8 mm.

In a biaxial extruder having a screw diameter of 45 mm, which provides a rotational velocity of the screw being 200 rpm, and having L/D of 35, a type B resin composition shown in Table 5 below was obtained. Temperature in the die during extrusion of the resin composition was from 180° C. to 230° C. The core was covered by this resin composition therearound with injection molding to obtain a mid layer. This mid layer had a thickness Tm of 1.2 mm, and a hardness Hm of 42.

An aqueous solution of carboxyl group-containing polyurethane (trade name “W-615”, available from Mitsui Takeda Chemicals, Inc.) in an amount of 100 parts by weight was mixed with 10 parts by weight of a water dispersion liquid of polycarbodiimide (trade name “Carbodilite® E-03A”, supra). This aqueous solution of carboxyl group-containing polyurethane had an acid value of 9 mg KOH/g, and a solid content of 35% by weight. This water dispersion liquid of polycarbodiimide had a carbodiimide equivalent of 365, and a solid content of 40% by weight. This mixture was applied on the mid layer by a spray gun to obtain a reinforcing layer having a thickness of 0.008 mm.

A type F resin composition shown in Table 5 below was obtained in the aforementioned biaxial extruder. Half shell was obtained from this resin composition with compression molding. The spherical body composed of the core, the mid layer and the reinforcing layer was covered by two pieces of the half shell, and placed into a mold having upper and lower mold half each having a hemispherical cavity to obtain a cover by compression molding. The cover had a thickness Tc of 0.8 mm. A paint layer was formed around this cover to give a golf ball of Example 12. This golf ball had a diameter of 42.8 mm.

Examples 14 to 15 and Comparative Example 5

In a similar manner to Example 12 except that the diameter of the core and the thickness of the cover were as listed in Table 6 below, golf balls of Examples 14 to 15 and Comparative Example 5 were obtained.

Example 13 and Comparative Example 6

In a similar manner to Example 12 except that the diameter of the core and the thickness of the mid layer were as listed in Table 6 below, golf ball of Example 13 was obtained. In a similar manner to Example 12 except that a type y rubber composition was used for the core, and that the diameter of the core and the thickness of the mid layer were as listed in Table 6 below, golf ball of Comparative Example 6 was obtained. Details of the type y rubber composition are shown in Table 1 above.

Comparative Example 7

In a similar manner to Example 1 except that the type of the resin composition of the cover was as listed in Table 7 below, golf ball of Comparative Example 7 was obtained. Details of the resin composition are shown in Table 5 below.

Examples 16 to 18

In a similar manner to Example 12 except that the type of the resin composition of the mid layer was as listed in Table 7 below, golf balls of Examples 16 to 18 were obtained. Details of the resin composition are shown in Table 5 below.

Example 19

In a similar manner to Example 1 except that a coating composition comprising a two-component cured epoxy resin as the base polymer (trade name “POLIN 750LE”, available from Shinto Paint Co., Ltd.) was used for forming the reinforcing layer, golf ball of Example 19 was obtained. This coating composition was prepared by mixing 100 parts by weight of the base material with 100 parts by weight of the curing agent. This base material contains a 30% by weight bisphenol A type epoxy resin and a 70% by weight solvent. This curing agent contains 40% by weight modified polyamide amine, 5% by weight titanium dioxide, and a 55% by weight solvent.

Comparative Example 8

In a similar manner to Example 12 except that the reinforcing layer was not provided, golf ball of Comparative Example 16 was obtained.

[Evaluation]

Similarly to the aforementioned Experiment 1, the amount of compressive deformation, the durability, the flight distance and the feel at impact of the golf balls were evaluated. The results are presented in Table 6 and Table 7 below. In connection with the durability, indices on the basis of the value in Comparative Example 8 being presumed as 100 are presented in Table 6 and Table 7 below.

TABLE 5 Specifications of mid layer and cover (part by weight) Type A B C D E F Surlyn 8945 18 26 33 35 40 45 Surlyn 9945 18 26 33 35 40 45 Rabalon SR04 64 48 34 30 20 10 Titanium dioxide 4.0 4.0 4.0 4.0 4.0 4.0 Ultra Marine Blue 0.1 0.1 0.1 0.1 0.1 0.1 Hardness (Shore D) 28 42 48 50 56 60

TABLE 6 Results of evaluation Example Example Example Example Compara. Compara. 13 14 12 15 Example 5 Example 6 Core Type x x x x x y Diameter (mm) 39.8 39.4 38.8 38.4 38.0 37.4 Mid Type B B B B B B layer Hardness (Shore D) 42 42 42 42 42 42 Thickness (mm) 0.7 1.2 1.2 1.2 1.2 1.9 Reinforcing Base Polymer water- water- water- water- water- water- layer based based based based based based urethane urethane urethane urethane urethane urethane Cover Type F F F F F F Hardness (Shore D) 60 60 60 60 60 60 Thickness (mm) 0.8 0.5 0.8 1.0 1.2 0.8 Amount of compressive 3.3 3.4 3.4 3.4 3.3 3.3 deformation (mm) of ball Durability 133 135 138 140 139 138 Travel distance (m) 257 258 256 253 246 245 Feel at impact A A A A C B

TABLE 7 Results of evaluation Compara. Example Example Example Example Compara. Example 7 16 17 18 19 Example 8 Core Type x x x x x x Diameter (mm) 38.8 38.8 38.8 38.8 38.8 38.8 Mid Type B A C E B B layer Hardness (Shore D) 42 28 48 56 42 42 Thickness (mm) 1.2 1.2 1.2 1.2 1.2 1.2 Reinforcing Base Polymer water- water- water- water- epoxy — layer based based based based urethane urethane urethane urethane Cover Type D F F F F F Hardness (Shore D) 50 60 60 60 60 60 Thickness (mm) 0.8 0.8 0.8 0.8 0.8 0.8 Amount of compressive 3.5 3.6 3.3 3.2 3.4 3.4 deformation (mm) of ball Durability 140 133 140 143 132 100 Travel distance (m) 240 249 254 253 254 247 Feel at impact B B B B A A

As is clear from Table 6 and Table 7, the golf balls of Examples are excellent in all terms of the durability, flight performance and feel at impact. Therefore, advantages of the present invention are clearly suggested by these results of evaluation.

The foregoing description is just for illustrative examples, therefore, various modifications can be made in the scope without departing from the principles of the present invention. 

1. A golf ball which comprises a spherical core, amid layer positioned outside of the core, a reinforcing layer positioned outside of the mid layer, and a cover positioned outside of the reinforcing layer, said core having a diameter of 39.2 mm or greater and 41.0 mm or less, said mid layer having (1) a hardness Hm as measured with a Shore D type hardness scale of equal to or less than 54 and (2) a thickness Tm of 0.5 mm or greater and 1.2 mm or less, and said cover having (1) a hardness Hc as measured with a Shore D type hardness scale of equal to or greater than 56 and (2) a thickness Tc of 0.8 mm or less.
 2. The golf ball according to claim 1, wherein said cover has a weight Wc of equal to or less than 4.0 g.
 3. The golf ball according to claim 1, wherein said cover has a ratio (Wc/Hc) of the weight Wc to the hardness Hc of equal to or less than 0.080.
 4. The golf ball according to claim 1, wherein said mid layer has the hardness Hm of equal to or greater than
 30. 5. The golf ball according to claim 1, wherein said cover has the thickness Tc equal to or less than 0.5 mm.
 6. The golf ball according to claim 1, wherein said cover has the hardness Hc of equal to or less than
 65. 7. The golf ball according to claim 1, wherein said reinforcing layer comprises a water-based adhesive
 8. A golf ball according to claim 7, wherein said water-based adhesive comprises a base polymer which is a reaction product between a carboxyl group-containing polyurethane and a polycarbodiimide.
 9. The golf ball according to claim 1, wherein said reinforcing layer has a thickness of 0.003 mm or greater and 0.050 mm or less.
 10. The golf ball according to claim 1, wherein a base polymer of said reinforcing layer is a reaction product between carboxyl group-containing polyurethane and polycarbodiimide.
 11. The golf ball according to claim 10, wherein said carboxyl group-containing polyurethane and said polycarbodiimide are water-based.
 12. The golf ball according to claim 1, wherein the principal component of a base polymer of said cover is an ionomer resin.
 13. The golf ball according to claim 12, wherein the base polymer of the cover comprises a styrene block-containing thermoplastic elastomer.
 14. The golf ball according to claim 13, wherein the base polymer of the cover comprises 10% by weight or less styrene block-containing thermoplastic elastomer.
 15. The golf ball according to claim 1, wherein a base polymer of the mid layer comprises 10% by weight or more styrene block-containing thermoplastic elastomer, and 40% by weight or more ionomer resin.
 16. The golf ball according to claim 15, wherein the base polymer of the mid layer comprises 10% by weight or more and 60% by weight or less of a styrene block-containing thermoplastic elastomer, and 40% by weight or more and 90% by weight or less of an ionomer resin.
 17. The golf ball according to claim 16, wherein the base polymer of the mid layer comprises 30% by weight or more and 60% by weight or less styrene block-containing thermoplastic elastomer, and 40% by weight or more and 70% by weight or less ionomer resin.
 18. The golf ball according to claim 15, wherein the styrene block-containing thermoplastic elastomer of the mid layer is an alloy of olefin and one or two or more selected from the group consisting of SBS, SIS, SEBS, SEPS and SEEPS, and hydrogenated products thereof.
 19. The golf ball according to claim 1, wherein the golf ball has a diameter greater than 42.67 mm. 